The goal of this project is to better understand the effects of host cells and other co-factors on human retroviral replication and pathogenesis. After development of the infectious molecular clone of Human T cell Leukemia/Lymphoma virus type I (HTLV-I), we determined that cell-free infection results in cytokine dependent transformation and that p12 and p30 open reading frames of HTLV-I are not needed for transformation. It is now clear that HTLV, HIV and Human Foamy Virus, there is a balance between productive infection and latent infection. In AIDS patients, we and others has found that this equilibrium can upset by immune stimulation and methylation. We are studying the pathogenic consequences of altering this balance using T cells and monocyte/ macrophages. Monocytes from asymptomatic HIV+ individuals contained latent HIV. After coculture of these monocytes with Con A-activated T-cells from HIV negative normal donors, these monocytes expressed virus. In latently infected THP-1, infectious virus was made after 5-azacytidine exposure. Since this suggests that cellular methylation plays a role in HIV replication, we studied whether HIV infection could result in aberrant methylation of cellular genes. A significant increase in the de novo methylation of the IFN-gamma promoter, which correlated with decreased expression, was seen in these acutely infected cells. A CD4+ lymphoid cell line-JMO, which expresses IFN-gamma constitutively, was stablely transfected using expression vectors containing DNA MTase cDNA in the antisense orientation (TMH). RNase protection analyses demonstrated a significantly lower level of MTase expression in the JMO expressing antisense MTase. Southern analysis showed hemimethylation of the IFN-gamma promoter in the JMO cell line expressing the parental neo construct while JMO-TMH was completely hypomethylated. IFN-gamma production in cell line constitutively producing MTase antisense, JMO-TMH, was significantly higher than a cell line constitutively expressing the parental vector. After acute infection of HIV, HIV-1 expression was greatly reduced in JMO-TMH presumably due to the high level of IFN-gamma. Since IFN-gamma plays a major role in host defense against viral infection, hypermethylation of the promoter which results in decreased IFNgamma production is one mechanism by which HIV-1 evades the immune response.